Steam-cracking is one of the most widely used basic petrochemical processes. It is used by industries to produce light olefins such as ethylene, propylene, butenes and butadiene and it is also relied upon for the production of aromatics such as benzene, toluene and xylenes.
Basically, steam-cracking comprises a step in which the hydrocarbon mixture to be transformed is mixed with steam and submitted to elevated temperatures in a tubular reactor. The different resulting products, gaseous and liquid hydrocarbons are then collected and separated. Thus, product distribution depends on the nature of the initial hydrocarbon mixture as well as experimental conditions.
Among the products obtained, C.sub.2 -C.sub.4 light olefins, as well as benzene, toluene, ethylbenzene and xylenes have the highest commercial values and since enormous quantities are processes throughout the world, even small yield improvements lead to substantial profit increases.
In recent years, ZSM-5 zeolite catalysts have drawn considerable attention because of their ability to increase selectivity in a variety of industrial processes such as xylene isomerization, toluene disproportionation, aromatic alkylation and methanol conversion.
It has been shown that the zeolite's selectivity properties are the result of its tridimensional channel network and of the different pore sizes of its structure.
One of the most interesting areas where ZSM-5 zeolites have shown substantial catalytic activity is in the process in which methanol is converted into hydrocarbons. Thus, by using appropriate reaction conditions, very high yields in C.sub.5 -C.sub.11 gasoline hydrocarbons can be obtained. However, this reaction presents the drawback of producing small quantities of durene, an undesirable reaction product.
Furthermore, modifications of the catalyst can also lead to highly efficient production of light olefins resulting from methanol conversion.
Thus, it can be seen that modified zeolite catalysts have the possibilities to present very interesting properties for enhancing yields in petrochemical reactions.
Therefore, since steam-cracking is one of the most widespread petrochemical processes, it would be highly desirable to provide means for increasing production of the most valuable reaction products.